arXiv subjects

Zhi-Yuan Zhou

Publications and source records attributed to Zhi-Yuan Zhou.

At least 73 records · Page 4Linked to original sources

arXiv2016

Orbital angular momentum-entanglement frequency transducer

Entanglement is a vital resource for realizing many tasks such as teleportation, secure key distribution, metrology and quantum computations. To effectively build entanglement between different quantum systems and share information between them, a frequency transducer to convert between quantum states of different wavelengths while retaining its quantum features is indispensable. Information encoded in the photons orbital angular momentum OAM degrees of freedom is preferred in harnessing the information carrying capacity of a single photon because of its unlimited dimensions. A quantum transducer, which operates at wavelengths from 1558.3 nm to 525 nm for OAM qubits, OAMpolarization hybrid entangled states, and OAM entangled states, is reported for the first time. Nonclassical properties and entanglements are demonstrated following the conversion process by performing quantum tomography, interference, and Bell inequality measurements. Our results demonstrate the capability to create an entanglement link between different quantum systems operating in photons OAM degrees of freedoms, which will be of great importance in building a high capacity OAM quantum network.

quant-ph↗

arXiv2016

High-dimensional entanglement between distant atomic ensemble memories

Entangled quantum states in high-dimensional space show many advantages compared with entangled states in two-dimensional space. The former enable quantum communication with higher channel capacity, enable more efficient quantum-information processing, and are more feasible for closing the detection loophole in Bell test experiments. Establishing high-dimensional entangled memories is essential for long-distance communication, but its experimental realization is lacking. We experimentally established high-dimensional entanglement in orbital angular momentum space between two atomic ensembles separated by 1 m. We reconstructed the density matrix for a three-dimensional entanglement and obtained an entanglement fidelity of 83.9+/-2.9%. More importantly, we confirmed the successful preparation of a state entangled in more than three-dimensional space (up to seven-dimensional) using entanglement witnesses. Achieving high-dimensional entanglement represents a significant step towards a high-capacity quantum network.

quant-ph↗

arXiv2016

Storing a single photon as a spin wave entangled with a flying photon in telecomband

Quantum memory is an essential building block for quantum communication and scalable linear quantum computation. Storing two color entangled photons, with one photon being at telecom-wavelength while the other photon being compatible of quantum memory, has great advantages toward the realization of the fiber based long-distance quantum communication with the aid of quantum repeaters. Here, we report an experimental realization of storing a photon entangled with a telecom photon in polarization as an atomic spin wave in a cold atomic ensemble, thus establishing the entanglement between the telecom-band photon and the atomic ensemble memory in polarization degree of freedom. The reconstructed density matrix and the violation of Clauser Horne Shimony Holt inequality clearly show the preservation of quantum entanglement during storage. Our result is very promising for establishing a long-distance quantum network based on cold atomic ensembles.

quant-ph↗

arXiv2015

Two-color ghost interference with photon pairs generated in hot atoms

We report on an experimental observation of a two-photon ghost interference experiment. A distinguishing feature of our experiment is that the photons are generated via a non-degenerated spontaneous four-wave mixing process in a hot atomic ensemble; therefore the photon has narrow bandwidth. Besides, there is a large difference in frequency between two photons in a pair. Our works may be important to achieve more secure, large transmission capacity long-distance quantum communication.

quant-ph↗

arXiv2015

CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer

A polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum swapping, quantum computation and high precision quantum metrology. Here, we report on the generation of a continuous-wave pumped degenerated 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II phase-matched periodically poled KTiOPO4 crystal in a Sagnac interferometer. Hong-Ou-Mandel-type interference measurement shows the photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The wavelength of photons can be tuned over a broad range by changing the temperature of crystal or pump power without losing the quality of entanglement. This source will be useful for building up long-distance quantum networks.

quant-ph↗

arXiv2015

Non-destructive splitter of twisted light

Efficiently discriminating beams carrying different orbital angular momentum (OAM) is of fundamental importance for various applications including high capacity optical communication and quantum information processing. We design and experimentally verify a distinguished method for effectively splitting different OAM-carried beams by introducing Dove prisms in a ring cavity. Because of rotational symmetry broken of two OAM-carried beams with opposite topological charges, their transmission spectra will split. When mode and impedance matches between the cavity and one OAM-carried beam are achieved, this beam will transmit through the cavity, and other beam will be reflected without being destroyed their spatial shapes. In this case, the cavity acts like a polarized beam splitter. The transmitting beam can be selected at your will. The splitting efficiency can reach unity if the cavity is lossless and it completely matches with the beam. Beams carry multi-OAMs can also be effectively split by cascading ring cavities.

physics.optics↗

arXiv2015

Orbital angular momentum photonic quantum interface

Light carrying orbital angular momentum (OAM) has great potential in enhancing the information channel capacity in both classical and quantum optical communications. Long distance optical communication requires the wavelengths of light are situated in the low-loss communication windows, but most quantum memories currently being developed for use in a quantum repeater work at different wavelengths, so a quantum interface to bridge the wavelength gap is necessary. So far, such an interface for OAM-carried light has not been realized yet. Here, we report the first experimental realization of a quantum interface for a heralded single photon carrying OAM using a nonlinear crystal in an optical cavity. The spatial structures of input and output photons exhibit strong similarity. More importantly, single-photon coherence is preserved during up-conversion as demonstrated.

quant-ph↗

arXiv2015

Magnetic-field-induced rotation of light with orbital angular momentum

Light carrying orbital angular momentum (OAM) has attractive applications in the fields of precise optical measurements and high capacity optical communications. We study the rotation of a light beam propagating in warm 87Rb atomic vapor using a method based on magnetic-field-induced circular birefringence. The dependence of the rotation angle on the magnetic field makes it appropriate for weak magnetic field measurements. We quote a detailed theoretical description that agrees well with the experimental observations. The experiment shown here provides a method to measure the magnetic field intensity precisely and expands the application of OAM-carrying light. This technique has advantage in measurement of magnetic field weaker than 0.5 Gauss, and the precision we achieved is 0.8 mGauss.

quant-ph↗

arXiv2015

Dynamic mode evolution and phase transition of twisted light in nonlinear process

We report on studying the dynamic evolution of orbital angular momentum (OAM) carrying light in sum frequency generation (SFG). Dynamic evolution of the SFG beam is studied in different cases, in which the two pump beams are either a single OAM mode or OAM superposition mode. For the cases when the two pumps are both in superposition mode, two kinds of spatial patterns and evolution behaviors are observed, one set of spatial pattern is non-diffractive and unchanged with propagating. In addition, SFG of two pump beams with opposite OAM will evolve into a kind of quasi-Gaussian mode. These observations show that the pumps phases are coherently transferred to SFG beam in the conversion process. Our findings give insights to physical picture of OAM light transformation in nonlinear processes, which can be used in OAM mode engineering and de-multiplexing of different OAM modes.

physics.optics↗

arXiv2015

Tunable cavity-enhanced photon pairs source in Hermite-Gaussian mode

The spatial modes of light have grasped great research interests because of its great potentials in optical communications, optical manipulation and trapping, optical metrology and quantum information processing. Here we report on generating of photon pairs in Hermite-Gaussian (HG) mode in a type-I optical parametric oscillator (OPO) operated far below threshold. The bandwidths of the photon pairs are 11.4 MHz and 20.8MHz for two different HG modes respectively, which is capable to be stored in cold Rubidium atomic ensembles. From correlation measurements, non-classical properties of HG modes in different directions are verified by tuning the cavity. Our study provides an effective way to generate photon pairs with narrow bandwidth in high order spatial modes for high dimensional quantum communication.

quant-ph↗

arXiv2015

A classical to quantum optical network link for orbital angular momentum carrying light

Light with orbital angular momentum (OAM) has great potentials in both classical and quantum optical communications such as enhancing the transmission capacity of a single communication channel because of its unlimited dimensions. Based on OAM conservation in second order nonlinear interaction processes, we create a classical to quantum optical network link in OAM degree of freedoms of light via sum frequency generation (SFG) following by a spontaneous parametric down conversion (SPDC). A coherent OAM-carrying beams at telecom wavelength 1550nm is up-converted to 525.5nm OAM-carrying beams in the first crystal, then up-converted OAM-carrying beam is used to pump a second crystal to generate non-degenerate OAM entangled photon pairs at 795nm and 1550nm. By switching the OAM carries by the classical party, the OAM correlation in the quantum party is shifted. High OAM entanglements in two dimensional subspaces are verified. This primary study enables to build a hybrid optical communication network contains both classical and quantum optical network nodes.

quant-ph↗

arXiv2015

Experimental generation of tripartite telecom photons via an atomic ensemble and a nonlinear waveguide

Non-classical multi-photon and number states attracts many people because of their wide applications in fundamental quantum mechanics tests, quantum metrology and quantum computation, therefore it is a longstanding aim to generate such states experimentally. Here, we prepare photon triplets by using the spontaneously Raman scattering process in a hot atomic ensemble cascaded by the spontaneous parametric down conversion process in a periodical poled nonlinear waveguide, the strong temporal correlations of these three photons are observed. Our experiment represents the first combination of the different order nonlinear processes and different physical systems, showing the feasibility of such composite system in this research direction. In addition, the all photons in the prepared genuine triplet are in telecom band make them be suitable for long-distance quantum communication in optical fibre.

quant-ph↗

arXiv2014

Raman Quantum Memory of Photonic Polarised Entanglement

Quantum entanglement of particles is regarded as a fundamental character in quantum information, in which quantum state should be given for whole system instead of independently describing single particle. Constructing quantum memory of photonic entanglement is essential for realizing quantum networks, which had been performed previously by many memory protocols. Of which Raman quantum memory gives advantages in broadband and high-speed properties, resulting in huge potential in quantum network and quantum computation. However, Raman quantum memory of photonic polarised entanglement is a challenge work and still missing. Here, we report two Raman quantum memories based on gas atomic ensembles: 1. Heralded Raman quantum memory of hybrid entanglement of path and polarization of single photon. 2. Raman storage of two-particle photonic polarised entangled state. Our experimental performances of these two different Raman quantum storages of photonic entanglement show a very promising prospective in quantum information science.

quant-ph↗

arXiv2014

Observation of optical filtering effects with four-wave mixing in a cold atomic ensemble

We observe an optical filtering effect in four-wave mixing (FWM) process based on a cold atomic gas. The side peaks appear at the edges of pulse of generated optical field, and they propagate through the atomic media without absorption. The theoretical analysis shows that these side peaks corresponded to the high frequency part of pulse of generated signal, which means the atoms cannot response to the rapid change of the electromagnetic field in time. On the contrary, the low frequency components of generated signal are absorbed during the transmission through the atoms. In addition, we experimentally demonstrate that the backward side peak could be stored by using Raman transition in atomic ensemble and retrieved later.

quant-ph↗

arXiv2014

Frequency up-conversion and arbitrary sum arithmetic of lights with orbital angular momentum

Frequency sum of two light beams carrying orbital angular momentum (OAM) in quasi-phase matching crystals was reported for the first time. The situations in which one light carried OAM and the other is in Gaussian mode and both beams carried OAM were studied in detail. An arbitrary sum arithmetic of lights with OAM was demonstrated in the conversion process. Our study is very promising in constructing hybrid OAM-based optical communication networks and all optical switching.

physics.optics↗

arXiv2014

High efficiency SHG of orbital angular momentum light in an external cavity

Traditional methods for generating orbital angular momentum (OAM) light include holographic diffraction gratings, vortex phase plate and spatial light modulator. In this article, we report a new method for high efficient OAM light generation. By pumping an external cavity contains a quasi phase matching nonlinear crystal with a fundamental OAM carrying light and properly aligning the cavity, mode matching between the pump light and the cavitys higher order Laguerre-Gaussian (LG) mode is achieved, conversion efficiency up to 10.3 percentage have been obtained. We have demonstrated that the cavity can stably operate at its higher order LG mode just as Gaussian mode for the first time. The SHG light possesses a doubled OAM value with respect to the pump light. The parameters that affect the beam quality and conversion efficiency are discussed in detail. Our work opens a brand new field in laser optics, and makes the first step toward high efficiency OAM light processing.

physics.optics↗

arXiv2014

Generation of light with controllable spatial patterns via the sum frequency in quasi-phase matching crystals

Light beams with extraordinary spatial structures, such as the Airy beam (AB), the Bessel-Gaussian beam (BGB) and the Laguerre-Gaussian beam (LGB), are widely studied and applied in many optical scenarios. We report on preparation of light beams with controllable spatial structures through sum frequency generation (SFG) using two Gaussian pump beams in a quasi-phase matching (QPM) crystal. The spatial structures, including multi-ring-like BGB, donut-like LGB, and super-Gaussian-like beams, can be controlled periodically via crystal phase mismatching by tuning the pump frequency or crystal temperature. This phenomenon has not been reported or discussed previously. Additionally, we present numerical simulations of the phenomenon, which agree very well with the experimental observations. Our findings give further insight into the SFG process in QPM crystals, provide a new way to generate light with unusual spatial structures, and may find applications in the fields of laser optics, all-optical switching, and optical manipulation and trapping.

physics.optics↗

arXiv2014

Orbital angular momentum light frequency conversion and interference with quasi-phase matching crystals

Light with helical phase structures, carrying quantized orbital angular momentum (OAM), has many applications in both classical and quantum optics, such as high-capacity optical communications and quantum information processing. Frequency conversion is a basic technique to expand the frequency range of fundamental light. The frequency conversion of OAM-carrying light gives rise to new physics and applications such as up-conversion detection of images and high dimensional OAM entanglements. Quasi-phase matching (QPM) nonlinear crystals are good candidates for frequency conversion, particularly for their high-valued effective nonlinear coefficients and no walk-off effect. Here we report the first experimental second-harmonic generation (SHG) of OAM light with a QPM crystal, where a UV light with OAM of 100 is generated. OAM conservation is verified using a specially designed interferometer. With a pump beam carrying an OAM superposition of opposite sign, we observed interesting interference phenomena in the SHG light; specifically, a photonics gear-like structure is obtained that gives direct evidence of OAM conservation, which will be very useful for ultra-sensitive angular measurements. We also develop a theory to reveal the underlying physics of the phenomena. The methods and theoretical analysis shown here are also applicable to other frequency conversion processes, such as sum frequency generation and difference-frequency generation, and may also be generalized to the quantum regime for single photons.

physics.optics↗